The present invention relates to a motor-driven compressor, which is provided with a drive shaft and a motor. Pistons are driven by a swash plate, which is integrally rotated with the rotating shaft, for discharging refrigerant.
An example of a compressor that is driven by an electric motor has been disclosed in Japanese Unexamined Patent Publication No. Hei 5-187356. In this compressor, piston supports are moved by rotation of a swash plate, and pistons are driven by rotation of the swash plate. A guide groove is formed on a drive plate, which is fixed to a drive shaft, and a pivot pin attached to the swash plate engages the guide groove. A sleeve is supported on the drive shaft. The swash plate is supported to permit inclination by the sleeve through a pin. The inclination of the swash plate is guided by engagement with the guide groove and the pivot pin, and by axial movement of the sleeve. The compression reactive force generated when the refrigerant is discharged from the cylinder bore is received by the drive plate through the piston, the piston support, a thrust bearing, the swash plate, and the pivot pin.
The compression reactive force transmitted to the drive plate through the swash plate acts as a load torque with respect to the drive shaft of the compressor. A plurality of pistons are arranged at equal intervals around the drive shaft. The load torque with respect to one piston peaks when discharging refrigerant and is substantially zero when drawing refrigerant.
In a motor-driven compressor, a peak of a net torque, which is obtained by combining changes in the load torques with respect to the respective pistons, is generated by one of the pistons during one rotation of the drive shaft. If a peak of the net torque is largely different from the average value of the net torque, it is necessary to use a motor that generates a driving torque that exceeds the peak value of the net torque. Such a motor must be relatively large, which means the entire motor-driven compressor is relatively large.
The object of the present invention is to miniaturize the motor-driven compressor.
To attain the above-mentioned object, a motor-driven compressor that performs suction, compression, and discharge of a refrigerant is provided. The compressor includes a housing, a drive shaft, a swash plate, a transmission mechanism and a motor. The housing includes four cylinder bores separated by equal angular intervals. The pistons are located in the cylinder bores, respectively. The drive shaft is rotatably supported by the housing. The swash plate is integrally rotated with the drive shaft. The transmission mechanism transmits the rotation of the swash plate to the pistons. The motor drives the drive shaft. The ratio of the discharge pressure to the suction pressure when the discharge displacement of the compressor is maximum, that is, the compression ratio, is in a range of 2 to 4.5.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.